The present invention relates to components of catalysts for the polymerization of olefins, the catalysts obtained therefrom and the use of said catalysts in the polymerization of olefins CH2xe2x95x90CHR, in which R is hydrogen or an alkyl, cycloalkyl or aryl radical with 1-10 carbon atoms. Another aspect of the present invention relates to the polymers obtained using said catalysts.
Catalysts are known from the literature that are obtained from compounds MLx in which M is a transition metal, especially Ti, Zr and Hf, L is a ligand coordinating to the metal, x is the valence of the metal and at least one of the ligands L has cyclo-alkadienyl structure. Catalysts of this type using compounds Cp2TiCl2 or Cp2ZrCl2 (Cp=cyclopentadienyl) are described in U.S. Pat. Nos. 2,827,446 and 2,924,593. The compounds are used together with alkyl-Al compounds in the polymerization of ethylene. The catalytic activity is very low. Catalysts with very high activity are obtained from compounds Cp2ZrCl2 or Cp2TiCl2 and from their derivatives substituted in the cyclopentadienyl ring, in which the Cp ring can also be condensed with other rings, and from polyalumoxane compounds containing the repeating unit xe2x80x94(R)AlOxe2x80x94, in which R is a lower alkyl, preferably methyl (U.S. Pat. No. 4,542,199 and EP-A-129368).
Catalysts of the type mentioned above, in which the metallocene compound contains two indenyl or tetrahydro-indenyl rings bridge-bonded through lower alkylenes or through other divalent radicals, are suitable for the preparation of stereoregular polymers of propylene and other xcex1-olefins (EP-A-185918).
Stereospecific catalysts are also obtained from dicyclopentadienyl compounds in which the two rings are substituted differently with groups having steric hindrance such as to prevent rotation of the rings about the axis of coordination with the metal.
Substitution of indenyl or tetrahydroindenyl in suitable positions gives catalysts that have very high stereospecificity (EP-A-485823, EP-A-485820, EP-A-519237, U.S. Pat. No. 5,132,262 and U.S. Pat. No. 5,162,278).
The metallocene catalysts described above produce polymers with a very narrow molecular weight distribution (Mw/Mn of about 2).
Some of these catalysts also have the property of forming copolymers of ethylene with xcex1-olefins of the LLDPE type or ethylene/propylene elastomeric copolymers with very uniform distribution of the comonomer units. The LLDPE polyethylene obtained is further characterized by low solubility in solvents such as xylene or n-decane.
The polypropylene obtained with the highly stereospecific catalysts mentioned above has greater crystallinity and a higher deformation temperature compared with the polymer that can be obtained with the conventional Ziegler-Natta catalysts.
However, these metallocene catalysts have a considerable drawback with respect to the possibility of being employed in industrial processes for production of polyolefins that are not carried out in solution, owing to the fact that they are soluble in the reaction medium in which they are prepared and in the liquid medium of polymerization.
In order to be usable in gas-phase polymerization processes, the catalysts must be supported on suitable supports which endow the polymer with appropriate morphological properties.
Supports of various kinds have been used, including, among others, porous metal oxides such as silica or porous polymeric supports such as polyethylene, polypropylene and polystyrene. The halides of magnesium are also used as supports. In some cases magnesium halides are also used as counterion of an ion pair in which the metallocene compound supplies the cation and a compound, such as a Mg halide, supplies the anion.
When Mg halide is used for supplying the anion, the catalytic system is formed by the halide present in solid form and the metallocene compound dissolved in a solvent. A system of this type cannot be used in gas-phase polymerization processes. Mg halide is preferably used in finely divided form that can be obtained by grinding.
As support, Mg halide is used in pulverized form, obtainable by grinding. Catalysts obtained in this way are not of high performance. Sufficiently high yields can only be obtained when the Mg halide is used in a form in which it is partially complexed with an electron-donor compound, obtained by a special method of preparation.
Japanese Application No. 168408/88 (published on 12.7.1988) describes the use of magnesium chloride as support for metallocene compounds, such as Cp2TiCl2, Cp2ZrCl2, Cp2Ti(CH3)2 for forming, with trialkyl aluminium and/or polymethylalumoxane (MAO), catalysts for the polymerization of ethylene. The component containing the magnesium chloride is prepared by grinding MgCl2 with the metallocene compound, also working in the presence of electron-donor compounds. Alternatively, the component is prepared by treating the metallocene with a liquid MgCl2-alcohol adduct and subsequent reaction with AlEt2Cl. The catalyst activity, referred to MgCl2 is very low.
Catalysts comprising a metallocene compound of the type Cp2ZrCl2 supported on MgCl2 in spherical form and partially complexed with an electron-donor compound are described in U.S. Pat. No. 5,106,804. The performance of these catalysts is better than that described in Japanese Application No. 168408/88 but is still not satisfactory, since it is not possible to obtain polymers containing sufficiently low residues of the catalyst. The electron donor used must be free from atoms of active hydrogen and in addition must be uniformly distributed in the bulk of the Mg halide. Suitable supports cannot be obtained by mere mixing of the components. Homogeneous dispersion of the electron donor is obtained by forming the Mg halide (by halogenation of Mg-dialkyls) in the presence of a solvent containing the electron donor in dissolved form. The surface area of the Mg halide is not greater than 100 m2/g, and is preferably between 30 and 60 m2/g. No information is given with respect to the porosity of the support. The electron-donor compound is used in a quantity of from 0.5 to 15 mol % based on the Mg halide; its presence is necessary. The catalysts obtained have performance that is much lower than that of the corresponding unsupported catalysts in which the metallocene compound is used in solution.
Application EP-A-318048 describes catalysts in which a solid component comprising a compound of Ti supported on a magnesium chloride that has particular characteristics of surface area and of porosity and possibly an electron-donor compound, is used with benzyl compounds of Ti or Zr or with metallocene compounds of the type Cp2Ti(CH3)2 and bis-(indenyl)-Zr(CH3)2 for forming catalysts for polymerization of ethylene and of propylene. The weight ratio of metallocene to magnesium chloride is very high (greater than 1), so it is necessary to remove the metallocene from the obtained polymer. The catalysts are used in processes that are carried out in the presence of a liquid polymerization medium.
Application EP-A-439964 describes bimetallic catalysts suitable for the preparation of ethylene polymers with broad molecular weight distribution (Mw/Mn between 4 and 14) obtained by supporting a metallocene on a solid component containing a Ti compound supported on MgCl2. MAO or its mixtures with alkyl-Al are used as cocatalyst. Trialkyl-Al compounds are also used as cocatalysts but the catalytic activity is low. The yields of these mixed catalysts with active centres derived either from the Ti compound supported on MgCl2 or from the metallocene compound are very high when the catalysts are used in a hydrocarbon medium; on the other hand they are low when polymerization is effected in the gas phase. This is probably due to the fact that, when using a hydrocarbon medium, as the metallocene compound is not fixed to the support in a stable form, it dissolves in the hydrocarbon polymerization solvent. In practice, the obtained catalyst corresponds to a homogeneous catalyst in which the metallocene compound is used in solution. Working in the gas phase, the metallocene compound is present as a solid and the catalyst obtained therefrom has an activity lower than that of the corresponding catalyst used in solution.
Application EP-A-522281 describes catalysts obtained from Cp2ZrCl2 supported on MgCl2 and from mixtures of trialkyl-Al and compounds supplying stable anions of the type dimethylaniline-tetrakis-(pentafluorophenyl)-borate. The catalysts are prepared by grinding the components and are used to polymerize ethylene in the presence of a solvent (toluene) with good yields (based on MgCl2). In this case too, the metallocene compound is present largely in solution and not fixed to MgCl2 and the relatively high activity based on MgCl2 is due essentially to the catalyst dissolved in the polymerization medium.
Application EP-A-509944 describes catalysts using aniline-tetrakis-(pentafluorophenyl)-borate or Lewis acids such as MgCl2 together with metallocene halides pre-reacted with alkyl-Al compounds. The magnesium chloride is ground before being contacted with the pre-reacted metallocene compound. The yields of polymer based on the Mg halide are not high (less than about 100 g polymer/g MgCl2). The Mg halide has surface are between 1 and 300 m2/g, preferably between 30 and 300 m2/g. Mg chloride with area between 30 and 300 m2/g is obtained essentially by grinding the commercial chloride. In this case it is difficult for the area to exceed 100-150 m2/g and the porosities are relatively low (less than 0.1 cm3/g). Also in the case of the catalysts described in Application EP-A-509944 the yields should largely be attributed to the metallocene compound dissolved in the polymerization solvent.
Application EP-A-588404 describes catalysts obtained from metallocene compounds supported on Mg halides prepared by halogenation of dialkyl-Mg or alkyl-Mg halides with SiCl4 or SnCl4. The yields of polymer (polyethylene) per g of solid component and per g of Zr are relatively high, especially when the catalyst is obtained from MgCl2 prepared using SnCl4. Again in this case it is to be assumed that the high catalytic activity is due more to the catalyst derived from the metallocene compound that dissolves in the polymerization medium than from that derived from the metallocene compound actually supported on the Mg halide.
European Application EP-A-576213 describes catalysts obtained from a solution of MgCl2 in an alcohol, from a trialkyl-Al compound and from a metallocene compound. The yields of polymer are very low. The catalyst is practically inactive when the MgCl2 solution is replaced by solid MgCl2 activated by prolonged grinding.
Solid components have now unexpectedly been found that comprise a metallocene compound and a magnesium halide, capable of giving catalysts that have very high activity in the polymerization of olefins, characterized by surface area (BET method) greater than about 50 m2/g, porosity (BET method) greater than about 0.15 cm3/g and porosity (Hg method) greater than 0.3 cm3/g, with the proviso that when the surface area is less than about 150 m2/g, the porosity (Hg) is less than about 1.5 cm3/g.
The porosity and surface area according to the BET method are determined using the xe2x80x9cSORPTOMATIC 1800xe2x80x9d apparatus from Carlo Erba.
The porosity according to the Hg method is determined using a xe2x80x9cPorosimeter 2000 seriesxe2x80x9d porosimeter from Carlo Erba, following the procedure described below.
The porosity (BET) is preferably above 0.2 cm3/g and in particular between 0.3 and 1 cm3/g. The surface area (BET) is preferably greater than 100 m2/g and more preferably greater than 150 m2/g. A very convenient range is between 150 and 800 m2/g. Components with surface area less than 150 m2/g give catalysts with performance that is of interest, provided that the porosity (Hg method) is less than about 1.5 cm3/g, preferably between 0.4 and 1.2 cm3/g, and in particular between 0.5 and 1.1 cm3/g.
The components are preferably used in the form of spherical particles smaller than 150 xcexcm.
In the components with surface area (BET) less than 150 m2/g more than 50% of the porosity (BET) is due to pores with radius greater than 300 xc3x85 and preferably between 600 and 1000 xc3x85.
The components with surface area (BET) greater than 150 m2/g and in particular greater than 200 m2/g exhibit, along with porosity (BET) due to pores with radius between 300 and 1000 xc3x85, also porosity (BET) due to pores with radius between about 10 and 100 xc3x85. In general, more than 40% of the porosity (BET) is due to pores with radius greater than 300 xc3x85.
The mean dimensions of the crystallites of Mg halide present in the solid component are generally below 300 xc3x85 and more preferably below 100 xc3x85. The definition of the components of the invention also includes those components which, in normal conditions, do not display the values of area and porosity stated above but attain them after treatment with a solution of trialkyl-Al at 10% in n-hexane at 50xc2x0 C. for 1 hour.
The components of the invention are prepared by supporting a metallocene compound on a Mg halide or on a support containing Mg halide that has characteristics of surface area and of porosity that are within the ranges stated for the catalytic component.
In general the surface area (BET) and the porosity (BET) and porosity (Hg) of the starting magnesium halide are greater than those of the component obtained from it.
Preferred Mg halides have surface area (BET) greater than 200 m2/g and more preferably between 300 and 800 m2/g and porosity (BET) greater than 0.3 cm3/g.
The Mg halide can comprise, in smaller proportions, other components acting as co-support or used for improving the properties of the catalytic component. Examples of these components are AlCl3, SnCl4, Al(OEt)3, MnCl2, ZnCl2, VCl3, Si(OEt)4.
The Mg halide can be complexed with electron-donor compounds not containing active hydrogen in a quantity up to about 30 mol %, preferably 5-15 mol % based on the Mg halide. Examples of electron donors are ethers, esters, ketones.
The Mg halide can in its turn be supported on an inert support that has area and porosity such that the supported product has the values stated above. Suitable inert supports can be metal oxides such as silica, alumina, silica-alumina, possessing porosity (BET) greater than 0.5 cm3/g and surface area (BET) greater than 200 m2/g and for example between 300 and 600 m2/g.
Other inert supports can be porous polymers such as polyethylene, polypropylene and polystyrene.
Partially crosslinked polystyrene that has high values of surface area and porosity is particularly suitable.
Polystyrenes of this type are described in U.S. Pat. No. 5,139,985, whose description of the method of preparation and supporting of the magnesium halide is included here for reference. These polystyrenes generally have surface area (BET) between 100 and 600 m2/g and porosity (BET) greater than 0.5 cm3/g.
The amount of Mg halide that can be supported is generally between 1 and 20% by weight based on the mixture. The preferred Mg halide is Mg chloride. The Mg halide can be supported according to known methods, starting from its solutions in solvents such as tetrahydrofuran or by impregnation of the inert support with solutions of the halide in an alcohol; the alcohol is then removed by reaction with a compound such as a trialkyl-Al or dialkyl-Al halide or silicon halides. The alcohols used are generally alcohols with 1-8 carbon atoms.
A method that is very suitable for preparation of Mg halides that have the characteristics of porosity and area stated above, consists of reacting spherulized adducts of MgCl2 with alcohols, the said adducts containing from 0.1 to 3 mol of alcohol with alkyl-Al compounds, in particular triethyl-Al, triisobutyl-Al, AlEt2Cl.
A preparation of this type is described in U.S. Pat. No. 4,399,054 whose description is herein included for reference.
For the purpose of obtaining supports with morphological characteristics that are particularly suitable for gas-phase polymerization processes in a fluidized bed, the adduct of MgCl2 with about 3 mol of alcohol should be submitted, prior to reaction with the alkyl-Al, to a controlled partial dealcoholizing treatment such as that described in European Patent Application EP-A-553806, to which reference is made for the description. The Mg halides thus obtained have a spheroidal shape, mean dimensions less than 150 microns, surface area (BET) greater than 60-70 m2/g and generally between 60 and 500 m2/g.
Other methods of preparation of the Mg halides suitable for preparation of the components of the invention are those described in European Patent Application EP-A-553805, whose description is herein included for reference.
Supporting of the metallocene compound is carried out according to known methods by bringing the Mg halide into contact, for example, with a solution of the metallocene compound, operating at temperatures between room temperature and 120xc2x0 C. The metallocene compound that is not fixed on the support is removed by filtration or similar methods or by evaporating the solvent.
The amount of metallocene compound supported is generally between 0.1 and 5% by weight expressed as metal.
The atomic ratio of Mg to transition metal is generally between 10 and 200; it can, however, be less and reach values of 1 or even less when the Mg halide is supported on an inert support.
The metallocene compounds are sparingly soluble in hydrocarbons (the hydrocarbon solvents most used are benzene, toluene, hexane, heptane and the like). Their solubility increases considerably if the solvent contains a dissolved alkyl-Al compound such as triethyl-Al, triisobutyl-Al or a polyalkylalumoxane, in particular MAO (polymethyl-alumoxane) in molar ratios with the metallocene compound greater than 2 and preferably between 5 and 100.
Impregnation of the support starting from the. solution mentioned above makes it possible to obtain particularly active catalysts (the activity is greater than that of the catalysts that can be obtained from solutions of the metallocene compound that do not contain the alkyl-Al compound or MAO).
The metallocene compounds that can be used are selected from the compounds of a transition metal M selected from Ti, V, Zr and Hf containing at least one xcfx80bond between a transition metal and a cyclopentadienyl-group containing moiety and comprising preferably at least one ligand L coordinated on the metal M possessing a mono- or polycyclic structure containing conjugated xcfx80 electrons.
The said compound of Ti, V, Zr or Hf is preferably selected from components possessing the structure:
in which M is Ti, V, Zr or Hf; CpI and CpII, identical or different, are cyclopentadienyl groups, including substituted ones; two or more substituents on the said cyclopentadienyl groups can form one or more rings possessing from 4 to 6 carbon atoms; R1, R2 and R3, identical or different, are atoms of hydrogen, halogen, an alkyl or alkoxyl group with 1-20 carbon atoms, aryl, alkaryl or aralkyl with 6-20 carbon atoms, an acyloxy group with 1-20 carbon atoms, an allyl group, a substituent containing a silicon atom; A is an alkenyl bridge or one with structure selected from: 
which M1 is Si, Ge, or Sn; R1 and R2, identical or different, are alkyl groups with 1-4 carbon atoms or aryl groups with 6-10 carbon atoms; a, b, c are, independently, integers from 0 to 4; e is an integer from 1 to 6 and two or more of the radicals R1, R2 and R3 can form a ring. In the case when the Cp group is substituted, the substituent is preferably an alkyl group with 1-20 carbon atoms.
Representative compounds that have formula (I) include: (C5Me5)MMe3, (C5Me5)M(OMe)3, (C5Me5)MCl3, (Cp)MCl3, (Cp)MMe3, (C5MeH4)MMe3, (C5Me3H2)MMe3, (C5Me4H)MMe3, (Ind)MBenz3, (H4Ind)MBenz3, (Cp)MBu3.
Representative compounds that have formula (II) include: (Cp)2MMe2, (Cp)2MPh2, (Cp)2MEt2, (Cp)2MCl2, (Cp)2M(OMe)2, (Cp)2M(OMe)Cl, (C5MeH4)2MCl2, (C5Me5)2MCl2, (C5Me5)2MMe2, (C5Me5)2MMeCl, (Cp)(C5Me5)MCl2, (1-MeFlu)2MCl2, (Me5Cp5)2M(OH)Cl, (Me5Cp5)2M(OH)2, (C5BuH4)2MCl2, (C5Me3H2)2 MCl2, (C5Me4H)2 MCl2, (C5Me5)2 M(OMe)2, (C5Me5)2 M(C6H5)2, (C5Me5)2 M(CH3)Cl, (C5EtMe4)2MCl2, [(C6H5)C5Me4]2 MCl2, (C5Et5)2MCl2, (C5Me5)2M(C6 H5)Cl, (Ind)2MCl2, (Ind)2MMe2, (H4 Ind)2MCl2, (H4 Ind)2-MMe2, {[Si(CH3)3]Cp}2 MCl2, {[Si(CH3)3]2Cp}2 MCl2, (C5Me4H)( C5Me5)MCl2.
Representative compounds of formula (III) include: C2H4(Ind)2MCl2, C2H4(Ind)2MMe2, C2H4(H4Ind)2MCl2, C2H4(H4Ind)2MMe2, Me2Si(C5Me4H)2MCl2, Me2Si(C5Me4H)2MMe2, Me2SiCp2MCl2, Me2 SiCp2MMe2, Me2Si(C5Me4H)2MMeOMe, Me2Si(Flu)2MCl2, Me2Si(2-Et-5-iPrCp)2MCl2, Me2Si(H4Ind)2MCl2, Me2Si(H4 Flu)2MCl2, Me2SiCH2 (Ind)2MCl2, Me2Si(2-Me-H4Ind)2MCl2, Me2Si(2-MeInd)2MCl2, Me2Si(2-Et-5-iPr-Cp)2MCl2, Me2 Si(2-Me-5-EtCp)2MCl2, Me2 Si(2-Me-5-Me-Cp)2MCl2, Me2Si(2Me-4,5-benzoindenyl)2MCl2, Me2Si(4,5-benzoindenyl)2MCl2, Me2Si(2-EtInd)2MCl2, Me2Si(2-iPr-Ind)2MCl2, Me2Si(2-t-butyl-Ind)MCl2, Me2Si(3-t-butyl-5-MeCp)2MCl2, Me2Si(3-t-butyl-5-MeCp)2MMe2, Me2Si(2-MeInd)2 MCl2, C2H4(2-Me-4,5-benzoindenyl)2MCl2, Me2 C(Flu)CpMCl2, Ph2 Si(Ind)2MCl2, Ph(Me)Si(Ind)2MCl2, C2H4(H4Ind)M(NMe2)OMe, isopropylidene-(3-t-butyl-Cp)(Flu)MCl2, Me2C(C5Me4H)(C5MeH4)MCl2, Me2Si(Ind)2MCl2, Me2Si(Ind)2MMe2, Me2Si(C5Me4H)2MCl(OEt), C2H4(Ind)2M(NMe2)2, C2H4(C5Me4H)2MCl2 Me-Ind)2MCl2, C2H4(3-Me-Ind)2MCl2, C2H4(4,7-Me2-Ind)2MCl2, C2H4(5,6-Me2-Ind)2MCl2, C2H4(2,4,7-Me3Ind)2MCl2, C2H4(3,4,7-Me3Ind)2MCl2, C2H4(2-Me-H4Ind)2MCl1, C2H4(4,7-Me2-H4Ind)2MCl2, C2H4(2,4,7-Me3-H4Ind)2MCl2, Me2Si(4,7-Me2-Ind)2MCl2, Me2Si(-5,6-Me2-Ind)2MCl2, Me2Si(2,4,7-Me3-H4Ind)2MCl2.
In the simplified formulae given above, the symbols have the following meanings:
Me=methyl, Et=ethyl, iPr=isopropyl, Bu=butyl, Ph=phenyl, Cp=cyclopentadienyl, Ind=indenyl, H4Ind=4,5,6,7-tetra-hydroindenyl, Flu=fluorenyl, Benz=benzyl, M=Ti, Zr or Hf, preferably Zr.
Also preferred are metallocene compounds having the formula (Me5C5)2M(OH)Cl or (Me5C5)2M(OH)2, wherein m is a transition metal selected from Ti, V, Zr and Hf, Me=methyl and Cp=cyclopentadienyl.
Compounds of the type Me2Si(2-Me-Ind)2ZrCl2 and Me2Si(2-Me-H4Ind)ZrCl2 and their methods of preparation are described respectively in European Applications EP-A-485822 and 485820 whose description is included here for reference.
Compounds of the type Me2Si(3-t-butyl-5-MeCp)2ZrCl2 and of the type Me2Si(2-Me-4,5-benzoindenyl)ZrCl2 and their method of preparation are described respectively in U.S. Pat. No. 5,132,262 and in Patent Application EP-A-549900 whose description is included here for reference.
The components of the invention form, with alkyl-Al compounds or with polyalkyl-alumoxane compounds or their mixtures, catalysts that possess very high activity relative to the Mg halide.
The alkyl-Al compound is generally selected from compounds of formula AlR3, in which R is an alkyl that has 1-12 carbon atoms, and the alumoxane compounds containing the repeating unit xe2x80x94(R4)AlOxe2x80x94, in which R4 is an alkyl radical containing from 1 to 6 carbon atoms, and the said alumoxane compounds contain from 2 to 50 repeating units that have the formula described above. Typical examples of compounds that have the formula AlR3 are trimethyl-Al, triethyl-Al, triisobutyl-Al, tri-n-butyl-Al, trihexyl-Al, trioctyl-Al. Among the alumoxane compounds, use of MAO is preferable. Mixtures of alkyl-Al compounds, preferably triisobutyl- Al, and alumoxane compounds, preferably MAO, are also used advantageously.
When the transition metal compound containing at least one xcfx80 bond between a transition metal and a cyclopentadienyl-group containing moiety is of the type described in formulae (II) and (III), the compounds obtained from the reaction between AlR3 and H2O in molar ratios between 0.01 and 0.5 can be used advantageously.
In general the alkyl-Al compound is used in molar ratios relative to the transition metal between 10 and 5000, preferably between 100 and 4000, and more preferably between 500 and 2000.
The catalysts of the invention can be used for (co)polymerizing CH2=CHR olefins, in which R is hydrogen or an alkyl radical with 1-10 carbon atoms or an aryl.
They are used in particular for polymerizing ethylene and its mixtures with xcex1-olefins of the type stated above in which R is an alkyl radical.
The catalysts, particularly those obtained from compounds of the type C2H4(Ind)2ZrCl2, C2H4(H4Ind)ZrCl2 and Me2Si(Me4Cp)2ZrCl2, are suitable for producing LLDPE (copolymers of ethylene containing smaller proportions, generally below 20 mol %, of xcex1-olefin C3-C12) characterized by relatively low density values in relation to the content of xcex1-olefin, with reduced solubility in xylene at room temperature (below approx. 10% by weight) and with molecular weight distribution Mw/Mn between about 2.5 and 5.
The polypropylenes that can be obtained with the catalysts using a chiral metallocene compound are characterized by increased stereoregularity, high molecular weights that are easily controllable, and high degree of crystallinity.
The chiral metallocene compounds that can be used are for example of the type described in European Application EP-A-485823, EP-A-485820, EP-A-519237, and U.S. Pat. No. 5,132,262, and 5,162,278.
The following examples are given for the purpose of illustrating but not limiting the invention. The properties stated are determined in accordance with the following methods:
Porosity and surface area (BET): are determined according to BET methods (apparatus used: SORPTOMATIC 1800 from Carlo Erba). The porosity is calculated from the integral pore distribution curve in, function of the pores themselves.
Porosity and surface area with mercury: are determined by immersing a known quantity of the sample in a known quantity of mercury inside a dilatometer and then gradually increasing the pressure of the mercury hydraulically. The pressure of introduction of the mercury into the pores is a function of their diameter. Measurement is effected using a xe2x80x9cPorosimeter 2000 seriesxe2x80x9d porosimeter from Carlo Erba. The porosity, pore distribution and surface area are calculated from data on the decrease of volume of the mercury and from the values of the applied pressure.
The porosity and surface areas stated in the descriptions and in the examples are referred to pore dimensions up to 10000 xc3x85,
Size of the catalyst particles: is determined by a method based on the principle of optical diffraction of monochromatic laser light with the xe2x80x9cMalvern Instr. 2600xe2x80x9d apparatus. The average size is stated as P50.
Melt Index E (MIE): determined according to ASTM-D 1238, method E.
Melt Index F (MIF): determined according to ASTM-D 1238, method F.
Ratio of degrees (F/E): ratio between Melt Index F and Melt Index E.
Flowability: is the time taken for 100 g of polymer to flow through a funnel whose discharge hole has a diameter of 1.25 cm and whose walls are inclined at 20xc2x0 C. to the vertical.
Apparent density:. DIN 53194.
Morphology and granulometric distribution of the particles of polymer: ASTM-D 1921-63.
Fraction soluble in xylene: measured by dissolving the polymer in boiling xylene and determining the insoluble residue after cooling to 25xc2x0 C.
Content of comonomer: percentage by weight of comonomer determined from IR spectrum.
Density: ASTM-D 792.
Average size of MgCl2 crystallites [D(110)]: is determined from measurement of the width at half-height of the (110) diffraction line that appears in the X-ray spectrum of the magnesium halide, applying Scherrer""s equation:
D(110)=(Kxc2x71.542xc2x757.3)/(B-b)cosxcex8, in which:
K=constant (1.83 in the case of magnesium chloride);
B=half-width (in degrees) of the (110) diffraction line;
b=instrumental broadening;
xcex8=Bragg angle.
In the case of magnesium chloride, the (110) diffraction line appears at an angle 20xcex8 of 50.2xc2x0.